1. Field of the Invention
This invention generally relates to cryogenic storage apparatus and, more specifically, to unique features of the storage apparatus that allow the cryogenically stored sample to be removed from the cryogenic liquid for examination or manipulation without the risk of thawing the sample. This is especially important for any biological sample whose integrity would be damaged by thawing.
2. Description of the Prior Art
Cryogenic containers are used mainly for storage. When a cryogenically stored sample is removed from the cryogen, it must be processed immediately to prevent degradation of the sample before analysis. Often, the sample is removed from the cryogen and stored on ice until use. During handling, temporary storage on ice, or visual inspection, the sample often undergoes thawing. While it is often desired to preserve a sample beyond the initial evaluation or extraction of a subsample, the thaw-freeze-thaw cycle may be too destructive to sample integrity to permit return of the original sample to the cryogen for subsequent reuse.
Sitte (U.S. Pat. No. 4,578,963) discloses an apparatus for the cryofixation of specimens. The apparatus is designed to reduce the transfer of natural specimens through cold gaseous nitrogen to a minimum without incurring the risk of a detrimental accumulation of water, carbon dioxide and oxygen from the external room atmosphere on the liquid surface. The specimen is placed on a surface that is movable through a boundary between a cryogenic medium within a tank and an atmosphere external to the tank.
Fuhr et al. (U.S. Pat. No. 5,925,511) describes a method and apparatus for cryopreserving and cryogenically processing biological objects. The biological material is jetted in an enveloping solution in microdroplet form on a cooled substrate that causes the microdroplets to rapidly freeze. The substrate may contain surface structuring for maintaining the droplets in defined spacings or patterns. The frozen material is thereafter processed or stored at subfreezing temperatures.
Adam et al. [Crop Sci. 41:755-758 (2001)] disclose a nitrogen-chilled sample tray that allows cryogenically preserved samples to be sorted and measured without the risk of sample thawing. The tray comprises a stainless steel lid (working surface) brazed to a stainless steel pan, creating a reservoir designed to be filled with liquid nitrogen. The working surface is maintained at approximately the temperature of the liquid nitrogen. Practical limitations on the utility of the tray relate to the length of time (20-30 minutes) for the tray to reach the working temperature (xe2x88x92190xc2x0 C.), the relatively high volume (6-8 liters) of liquid nitrogen needed to reach the working temperature, and the frequency of liquid nitrogen replenishment needed to maintain the working temperature.
We have now invented a device comprising a cryogenically-cooled working surface for manipulating a frozen sample while efficiently maintaining the sample in a frozen state throughout the manipulation. This working surface is in heat exchange contact with a reservoir of cryogenic fluid. The reservoir is contained within an insulated vessel.
In accordance with this discovery, it is an object of the invention to provide a device for laboratory or field use comprising a cryogenic surface for working with a frozen sample while maintaining the frozen integrity of the sample.
It is also an object of the invention for the aforementioned device to be portable, positionally stable, and easily refillable with cryogenic fluid.
Another object of the invention is to provide a device having a cryogenic working surface that is rapidly brought to a useful working temperature and efficiently utilizes cryogenic fluid for maintaining that temperature for extended periods of time.
A further object of the invention is that the aforementioned device be easily and inexpensively manufactured.
These and other objects and advantages of the invention will become readily apparent from the ensuing description.